From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id C585EA052A; Fri, 10 Jul 2020 12:26:17 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 66AC11D9F9; Fri, 10 Jul 2020 12:26:17 +0200 (CEST) Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by dpdk.org (Postfix) with ESMTP id E27311D9AD for ; Fri, 10 Jul 2020 12:26:15 +0200 (CEST) IronPort-SDR: joAcJsMQrOKSY8W1pvVwmbkslhPcF5/UcolXpZ4iHh36NrPG3mXL8nqw2IaTaGAkY7pM4HtfuT 5D1ssWg2Fu1A== X-IronPort-AV: E=McAfee;i="6000,8403,9677"; a="233044540" X-IronPort-AV: E=Sophos;i="5.75,335,1589266800"; d="scan'208";a="233044540" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jul 2020 03:26:14 -0700 IronPort-SDR: oQkXPcDeFLA4s5ISpmDLV/Sr29lJmc1jbeDzGN8P9nN18sJKByr0heNN9SBab412yBuuZI+lnd 9/L8GCFsUBlw== X-IronPort-AV: E=Sophos;i="5.75,335,1589266800"; d="scan'208";a="458238174" Received: from bricha3-mobl.ger.corp.intel.com ([10.249.32.166]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-SHA; 10 Jul 2020 03:26:13 -0700 Date: Fri, 10 Jul 2020 11:26:09 +0100 From: Bruce Richardson To: Morten =?iso-8859-1?Q?Br=F8rup?= Cc: dev@dpdk.org, Olivier Matz Message-ID: <20200710102609.GA684@bricha3-MOBL.ger.corp.intel.com> References: <98CBD80474FA8B44BF855DF32C47DC35C61113@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <98CBD80474FA8B44BF855DF32C47DC35C61113@smartserver.smartshare.dk> Subject: Re: [dpdk-dev] Weird 2 KB MBUF data room requirement X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Fri, Jul 10, 2020 at 10:21:40AM +0200, Morten Brørup wrote: > Dear Ethernet PMD developers, > > According to rte_mbuf_core.h, RTE_MBUF_DEFAULT_DATAROOM is 2048 bytes because some NICs need at least 2 KB buffer to receive standard Ethernet frames without splitting them into multiple segments. > > This is a serious waste of memory, considering that standard Ethernet frames are max 1518 bytes. > > How wide spread is this limitation... is it common or a rare exception? > > Where is it documented which NICs suffer from this limitation? > > Do any Intel NICs suffer from this limitation? > > > NB: We are targeting an MBUF total size (incl. memzone element overhead) of 2^N, and this limitation would increase our MBUF total size to 4 KB. > > > Med venlig hilsen / kind regards > - Morten Brørup > AFAIK: the NICs supported by the ixgbe driver only allow the size to be specified in KB granularity. However, it may be safe to have a driver modification whereby anything over 1600 bytes is considered as 2KB if jumbo frame support is disabled. I don't think anyone has actually looked into doing so though, or if there are other hidden gotchas about attempting to do so. /Bruce